The present invention relates to a multifunction receiver capable of receiving radio waves from both of an electronic key system and a tire pressure monitoring system.
An electronic key system may be installed in a vehicle to verify an electronic key through wireless communication between the vehicle and the electronic key. A key-free operation system is a known electronic key system that performs narrowband wireless communication when, for example, receiving radio waves from a vehicle. Further, a tire pressure monitoring system (TPMS) may also be installed in a vehicle. In a tire pressure monitoring system, a tire pressure sensor is arranged in each tire to detect the air pressure of the tire. The tire pressure monitoring system receives a detection signal through wireless communication from each tire pressure sensor to monitor the air pressure of each tire.
In current systems, the frequency of the radio waves transmitted from an electronic key and the frequency of the radio waves transmitted from the tire pressure sensors are both set in the ultrahigh frequency (UHF) band. Further, to reduce the number of components, a receiver mounted on a body of a vehicle may be a multifunction receiver shared by the electronic key system and the tire pressure monitoring system (refer to, for example, Japanese Patent No. 4552995).
Such a multifunction receiver is operated in modes set in accordance with a smart reception request signal and a smart frequency switch signal provided from a verification electronic control unit (ECU) of the electronic key system. For example, the multifunction receiver is normally set in a TPMS communication mode and functions as a receiver for the tire pressure monitoring system. When the multifunction receiver receives the smart reception request signal from the verification ECU, the operation mode of the multifunction receiver is switched to a smart communication mode to function as a receiver for the electronic key system. In the smart communication mode, the multifunction changes a reception frequency when receiving the smart frequency switch signal from the verification ECU.
In case the smart reception request signal becomes fixed at a high level or a low level, the multifunction receiver will not be able to switch operation modes in a normal manner. Accordingly, there is a demand for a multifunction receiver that switches operation modes even when the smart reception request signal becomes fixed. The same problem also occurs when the smart frequency switch signal becomes fixed.